1. Field of the Invention
The present invention relates to a write head with counter current coil layers, and more particularly to a write head with first and second coil layers where the first coil layer is a write coil layer adjacent one side of a second pole piece layer and the second coil layer opposes the write coil layer on an opposite side of the second pole piece layer.
2. Description of the Related Art
A write head is typically combined with a magnetoresistive (MR) read head to form a merged MR head. A merged MR head may have thin film layers with edges that are exposed at an air bearing surface (ABS) for writing and receiving magnetic fields on a magnetic medium, such as a disk or tape drive. In a merged MR head, the write head comprises first and second pole piece layers connected at a back gap that is recessed from the ABS. Each of the first and second pole piece layers has a pole tip, a yoke and a back gap, with the yoke being located between the pole tip and the back gap. The pole tips, which may be referred to as first and second pole tips, terminate at the ABS. An insulation stack, which comprises a plurality of insulation layers, is sandwiched between the yoke portions of the first and second pole piece layers and a write coil layer is embedded in the insulation stack. A processing circuit is connected to the write coil layer for conducting a write current through the coil layer, which, in turn, induces magnetic flux in the first and second pole piece layers. A non-magnetic gap layer is sandwiched between the first and second pole tips so that magnetic flux in the first and second pole tips fringes across the gap layer at the ABS to create write fields.
In a magnetic disk drive a magnetic disk is rotated adjacent to and a short distance from the ABS so that the write fields magnetize the disk along circular tracks. The written circular tracks then contain magnetized segments with fields detectable by a read head.
An MR read head includes an MR sensor sandwiched between first and second non-magnetic gap layers and having an edge located at the ABS. The first and second gap layers and the MR sensor are sandwiched between first and second shield layers. In a merged MR head, the second shield layer and the first pole piece are a common layer. The MR sensor detects magnetic fields from the circular tracks of the rotating disk by a resistance change that corresponds to the strengths of the fields. A sense current conducted through the MR sensor results in voltage changes received by the processing circuitry as readback signals.
One or more merged MR heads may be employed in a magnetic disk drive for reading and writing information on circular tracks of a rotating disk. A merged MR head is mounted on a slider carried on a suspension. The suspension is mounted to an actuator which rotates the magnetic head to locations corresponding to desired tracks. As the disk rotates an air cushion is generated between the rotating disk and the ABS of the slider. A force of the air cushion against the ABS is opposed by an opposite loading force produced by the suspension, causing the magnetic head to be suspended a slight distance (flying height) from the surface of the disk. Flying heights are typically on the order of about 0.05 .mu.m.
A high data rate is desirable for high performance write heads. Data is written by the write head as field signals into the rotating disk. A high data rate increases the density of information recorded on the rotating disk. In digital recording, the circuit supplying write current to the write head is required to switch at a high rate to produce positive and negative field signals. The quicker the switching, the higher the data rate. Unfortunately the write current circuit's inductance limits the data rate. Furthermore high inductance requires a higher write circuit voltage. This decreases battery life of portable computers, and requires a thick write head coil to dissipate heat. A thicker coil increases the height of the write head in the yoke region, which increases the aspect ratio of a photolithography photoresist step employed for patterning the second pole tip. The aspect ratio is the ratio between the thickness of the photoresist in the pole tip region and the track width of the second pole tip. High aspect ratios result in poorly formed second pole tips.
The write coil layer is designed to have a certain turn density, pitch, spacing between the coil turns, thickness and overall diameter. Turn density is the number of coil turns per width across the coil. Pitch is the distance from the beginning of one coil turn to the beginning of an adjacent coil turn, as measured across the width of the coil and thickness is the thickness of the coil layer. The pole piece layers function as a core with respect to the write coil since they conduct the flux generated by the write coil. Upon energizing the write coil with write current, each coil turn generates flux that encircles the turn. Between first and second adjacent turns, the first turn generates flux in one direction in the space between the turns and the second turn generates flux in an opposite direction in the space between the turns. Consequently, flux from adjacent turns is cancelled in the space between the turns. However, flux from the turns above and below the coil layer combines to travel in one of two directions about the write coil layer, depending upon the polarity of the write current. Accordingly, flux about the coil layer is induced into each of the first and second pole piece layers, thereby providing write fields at the write gap.
It should be understood that the first and second pole pieces contribute to the inductance of the write current circuit. The inductance of this ferromagnetic circuit is proportional to the amount of flux conducted through it. This inductance is necessary because the ferromagnetic circuit will not work without the pole piece layers. However, there is also a certain amount of flux beyond the first and second pole piece layers that returns through the coil. This flux, known as "coil flux", is typically modelled as a parasitic inductance of the ferromagnetic circuit. The magnitude of this parasitic inductance is related to the amount of flux that travels through ferromagnetic material, such as the first pole piece layer beyond the ferromagnetic circuit or the first shield layer of the read head below the first pole piece. The magnitude of this parasitic inductance is also related to the pitch or the diameter of the write coil. However, reduction of the pitch or diameter increases the difficulty of manufacturing the write coil. If this parasitic inductance could be reduced, the frequency response of the write circuit could be increased to increase the data rate, the magnitude of the write current could be decreased to conserve power and reduce heat, the thickness of the write coil could be decreased, while pitch or diameter of the coil could be increased to promote manufacturability, and the first shield layer and the first pole piece layer could be extended beyond the back gap region to promote planarity of the head.